re_intuit_start(): check for IMPLICIT in stclass

re_intuit_start(): check for IMPLICIT in stclass

In the stclass block of code, there are various checks for anchored-ness.
Add !(prog->intflags & PREGf_IMPLICIT) to these conditions, since
from the perspective of these tests, we can only quit early etc if these
are real rather than fake anchors.

As it happens, this currently makes no logical difference, since an
PREGf_IMPLICIT pattern starts with .*, and so more or less by definition
can't have an stclass.

So this commit is really only for logical completeness, and to allow us to
change the definition of ml_anch shortly.